Force sensing semiconductive touchpad

ABSTRACT

A touchpad assembly and method for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad assembly is provided. The touchpad assembly includes X and Y position and pressure sensitive semiconductor resistance sensor layers. The X and Y sensors have a pair of spaced apart X and Y conductive traces running across opposite ends such that a resistance RX connects the pair of X traces and a resistance RY connects the pair of Y traces. The X and Y sensors come into contact at a contact point when an object asserts a pressure on the touchpad. The contact point is connected to each trace by a variable pressure resistance RZ associated with the X and Y sensors and variable position resistances of the X and Y resistances. First and second pair of timing capacitors are connected to respective ones of the pairs of X and Y traces. A microprocessor controls and monitors charging time of the capacitors to determine the position and asserted pressure of the object touching the touchpad.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.08/857,134, filed May 15, 1997, now U.S. Pat. No. 5,943,044, whichclaims the benefit of U.S. Provisional Application No. 60/023,168, filedAug. 5, 1996.

TECHNICAL FIELD

The present invention relates generally to object position sensingtransducers and systems and, more particularly, to semiconductivetouchpads.

BACKGROUND ART

Numerous devices are available as object position detectors for use incomputer systems and other applications. The most familiar of suchdevices is the computer mouse. While extremely popular as a positionindicating device, a mouse has mechanical pans and requires a surfaceupon which to roll its position ball. The mouse translates movement ofthe position ball across the rolling surface as input to a computer. Thegrowing popularity of laptop or notebook computers has created asignificant problem for mouse type technologies which require a rollingsurface. Laptop computers are inherently portable and designed for usein small confined areas such as, for example, airplanes, where there isinsufficient room for a rolling surface. Adding to the problem is that amouse usually needs to be moved over long distances for reasonableresolution. Finally, a mouse requires the user to lift a hand from thekeyboard to make the cursor movement, thereby upsetting the primepurpose, which is usually typing on the computer.

As a result of the proliferation of laptop computers and thestandardization of the Windows operating environment, a need for areliable, portable, and integrated form of mouse control has arisen. Tosatisfy this need, mechanical ball or shaft rolling technologies, suchas, for example, track balls have been designed for use with laptopcomputers. A track ball is similar to a mouse. A major difference,however is that, unlike a mouse, a track ball does not require a rollingsurface. Track balls first appeared as clip-on attachments for laptopcomputers and then later were integrated within laptop computers.

A track ball is large in size and does not fit well in avolume-sensitive application such as a laptop computer. Furthermore, atrack ball is quite cumbersome because it requires practiced dexterityby the user as he or she interacts with the device. Finally, a trackball is not durable and is easily subjected to contamination fromenvironmental factors such as dirt, grease, and the like.

A. Cursor Control with Touchpads

Touchpads are pointing devices used for inputting coordinate data tocomputers and computer-controlled devices. A touchpad is typically abounded plane capable of detecting localized pressure on its surface. Atouchpad may be integrated within a computer or be a separate portableunit connected to a computer like a mouse. When a user touches thetouchpad with a finger, stylus, or the like, the circuitry associatedwith the touchpad determines and reports to the attached computer thecoordinates or the position of the location touched. Thus, touchpads maybe used like a mouse as a position indicator for computer cursorcontrol. Several types of touchpads are known in the art such ascapacitive and resistive touchpads.

1. Capacitive Touchpads

Capacitive touchpads react to a capacitive coupling between an objectplaced near or on the surface of the touchpad and capacitors formedwithin the touchpad. For instance, U.S. Pat. No. 5,374,787 issued toMiller et al. and assigned to Synaptics, Inc., discloses a capacitivetouchpad having two thin layers of electrically conductive lines ortraces. A first set of traces runs in a first direction and is insulatedby a dielectric insulator from a second set of traces running in asecond direction generally perpendicular to the first direction. The twosets of traces are arranged in a crosswise grid pattern. The grid formedby the traces creates an array of capacitors that can store anelectrical charge.

When a conductive object such as a finger or a metal stylus approachesor touches the touchpad, the capacitance of the capacitors are altereddue to capacitive coupling between the object and the capacitors. Thedegree of alteration depends on the position of the object with respectto the traces. As a result, the location of the object in relation tothe touchpad can be determined and monitored as the object moves acrossthe touchpad.

Similarly, U.S. Pat. No. 3,921,166 issued to Volpe discloses a capartivematrix or grid in which an object such as a finger changes thetranscapacitance between row and column electrodes.

Another variation of the capacitive touchpad is shown in U.S. Pat. No.4,550,221 issued to Mabusth. The Mabusth patent discloses a capacitivetouchpad having a substrate that supports first and second interleaved,closely spaced, non-overlapping conducting plates. The plates arealigned in rows and columns so that edges of each plate of an array areproximate to, but spaced apart from, the edges of plates of the otherarray. The first and second arrays are periodically connected in amultiplexed fashion to a capacitance measuring circuit which measuresthe change in capacitance in the arrays. In effect, the Mabusth patentdiscloses a grid of pixels which are capacitively coupled.

Capacitive touchpads suffer from many disadvantages. First, they areextremely sensitive to moisture contamination. As an object such as afinger moves over the touchpad, the moisture present in the skindisturbs the capacitor grid and measurements made from the disturbancedetermines the position of the finger. The operation of capacitivetouchpads is, therefore, easily compromised in moist or dampenvironments or by perspiration of the user. In short, with moisture,capacitive touchpads become confused and lose their sensitivity.

Second, capacitive touchpads demand a constant power supply, offering nosleep mode option. Most capacitive touchpads draw a constant electricalcurrent of 2.5 to 10 milliamps whether or not they are in use. Withlaptops, cordless keyboards, and even hand-held remote controls, batterylife is a major concern. A touchpad that demands constant power is amajor liability.

Third, capacitive touchpads are prone to inadvertent cursor positioningbecause they sense an object as it gets near their surface. This isproblematic for the user because if the touchpad is installed near wherethe thumbs of the user naturally rest while typing, an inadvertent thumbsimply moving over and above the touchpad can cause a false click and anunintended change in the cursor position. This can result in repeated,accidental repositioning of the cursor and high levels of userfrustration. The user may also experience fatigue and extreme discomfortfrom intentionally holding his thumbs or fingers away from the touchpadto avoid false clicks.

Fourth, the electronic circuitry of capacitive touchpads is complex andexpensive. Capacitive touchpads use a microprocessor for communicatingwith a computer. Between the touchpad and the microprocessor, electroniccircuitry such as a semi-custom or fully-custom mixed signal gate arrayincorporating both analog and digital sections is provided. The cost ofthis circuitry is significant and, in most cases, higher than the costof the microprocessor.

Fifth, capacitive touchpads indirectly measure the amount of appliedpressure by measuring the surface area of the object applying thepressure. For instance, a capacitive touchpad measures the area ofcontact between a finger and the touchpad. Once that area is measured,relative pressure is determined by the change in the area over time.Illustratively, as a user pushes harder with his finger, more area is incontact and the touchpad estimates a greater pressure. Obviously, forapplications such as signature capture, pressure-controlled scrollingand acceleration, 3D control, and the like, measuring the contact areato estimate the pressure is greatly inferior to measuring the actualpressure directly.

2. Resistive Touchpads

U.S. Pat. No. 5,521,336 issued to Buchanan et al. discloses a typicalresistive touchpad. The disclosed resistive touchpad is a shunt modedevice where electrons flow between interdigitating conductive traceswhen the traces are pressed together. A voltage potential between theinterdigitating traces causes electrical current to flow through thetraces at the point where the traces are in electrical contact. Thelocation of the contact is determined using banks of drivers andreceivers which scan the resistive touchpad.

Resistive touchpads may include a resistive layer separating theinterdigitating traces at the point of contact. Thus, when a pair oftraces are pressed together against the resistive layer at a location,electrical current flows from one trace through the resistive layer tothe other trace at that location.

Resistive touchpads such as that disclosed by Buchanan et al. sufferfrom many disadvantages. First, resistive touchpads can only measureON/OFF resistance. Thus, they cannot measure gradation in pressure andcannot be used for such applications as signature capture,pressure-controlled scrolling and acceleration, 3D control, and thelike.

Second, the electronic circuitry of resistive touchpads is complex andexpensive. Like capacitive touchpads, resistive touchpads have amicroprocessor for communicating with a computer. Between the touchpadand the microprocessor, complex circuitry such as the banks of driversand receivers shown in Buchanan et al. are provided. The cost of thiscircuitry is significant and, in most cases, higher than the cost of themicroprocessor.

Third, resistive touchpads require a relatively significant force toactivate, roughly about twenty grams of force. Unfortunately for theuser, pushing his or her finger or a stylus against a touchpad at twentygrams of force is fatiguing.

B. Touchpads as Input Devices

In addition to cursor control, touchpads are also employed for providingcontrol signals to a computer to perform functions associated with thelocation pressed on the touchpad. Typically, one or more regions of atouchpad are assigned to certain functions. The user is made aware ofthe function associated with each region by a template. A template is asheet with a graphic design and is placed over and in contact with thetouchpad surface. The graphic design maps out regions of the touchpadsurface which are labelled to provide a reminder to the user as to thefunctions associated with the regions.

As an input device, a touchpad functions similarly to a mouse. Forinstance, a mouse generally has at least one mouse button foraccomplishing mouse controlled functions such as menu pull down andselection, icon selection and use, and the like. Sometimes more buttonshaving assigned functions are provided with a mouse. The various mappedregions of the touchpad may be associated with the assigned functions ofthe mouse.

A primary disadvantage of using prior art touchpads as input devices isthat the touchpads do not incorporate actual pressure data in theircontrol signals. It is desirable to control the rate that a computerperforms a function in proportion to the amount of actual pressure beingapplied to the input device. For example, if a user presses down in ascroll control region wanting a graphical user interface display toscroll, it is desirable that the rate of scrolling is proportional tothe amount of pressure applied. In short, more pressure should causefaster scrolling.

Furthermore, prior art touchpads are not user friendly. For instance,many portable touchpads include a button on the bottom of the touchpadwhich, when pressed, is used to emulate the selection function of thebutton on a mouse. When the user desires to drag the cursor across thedisplay, the button must be held down. When the cursor must be movedrelatively long distances, necessitating multiple touchpad strokes, itis difficult to hold the drag button down to prevent release of thebutton and termination of the drag sequence while accomplishing themultiple strokes. If the finger is simply lifted from the touchpad, thedrag sequence terminates and must be restarted. Even if the cursor canbe dragged with a single touchpad stroke, it is extremely difficult tomaintain sufficient pressure on the touchpad to hold the button downwhile sliding a finger across the touchpad. Consequently, in usingtouchpads for dragging, the drag sequences are frequentlyunintentionally terminated.

Summary of the Invention

Accordingly, it is an object of the present invention to provide atouchpad having the ability to measure the actual pressure applied by anobject and the location of the object touching the touchpad.

It is a further object of the present invention to provide a forcesensing semiconductive touchpad.

It is another object of the present invention to provide a force sensingsemiconductive touchpad having the ability to determine the position ofan object touching the touchpad.

It is yet a further object of the present invention to provide a forcesensing semiconductive touchpad having the ability to measure thegradation of pressure applied on the touchpad and offer dynamicpressure-sensing features.

It is yet another object of the present invention to provide a forcesensing semiconductive touchpad that requires minimal power consumption.

It is still yet a further object of the present invention to provide aforce sensing semiconductive touchpad having the characteristics ofrequiring minimal amount of force to be activated, not subjecting a userto fatigue, and not susceptible to inadvertent cursor positioning.

It is still yet another object of the present invention to provide aforce sensing semiconductive touchpad that is unaffected by ordinaryamounts of moisture occurring during use.

A further object of the present invention is to provide a force sensingsemiconductive touchpad that uses cheap and simple electronic circuitryfor determining the position and applied pressure of an object touchingthe touchpad.

Another object of the present invention is to provide a touchpad thatprovides a control signal having actual pressure data to a computer sothat the computer performs a function in proportion to the amount ofactual pressure being applied to the touchpad.

Still, a further object of the present invention is to provide atouchpad that is user friendly.

Still, another object of the present invention is to provide a touchpadhaving separate control regions linked to separate functions.

Still, yet a further object of the present invention is to provide atouchpad capable of gesture recognition for supporting single tap selectgesture, double tap execute gesture, and tap and drag dragging gestureto simulate actions done on a mouse button.

Still, yet another object of the present invention is to provide atouchpad having edge continuation motion for allowing large cursorexcursions with a relatively slight single gesture.

In carrying out the above objects, the present invention provides atouchpad for providing a signal to a computer. The signal is indicativeof the location and applied pressure of an object touching the touchpad.The touchpad includes a pad having a touch surface and a bottom surface.A first sensor layer is disposed adjacent the bottom surface of the pad.A first pair of spaced apart conductive traces runs across opposite endsof the first sensor layer in a first direction such that a firstresistance between the opposite ends of the first sensor layer connectsthe first pair of conductive traces.

The touchpad further includes a second sensor layer. A second pair ofspaced apart conductive traces runs across opposite ends of the secondsensor layer in a second direction generally perpendicular to the firstdirection such that a second resistance between the opposite ends of thesecond sensor layer connects the second pair of conductive traces. Thesecond sensor layer is disposed beneath the first sensor layer such thatthe first and second sensor layers come into contact at a contact pointwhen an object asserts a pressure on the touch surface of the pad. Thecontact point is connected to each conductive trace by a variablepressure resistance associated with the first and second sensor layersand variable position resistances of the first and second sensor layers.The variable pressure resistance varies inversely as a function of thepressure asserted and the variable position resistances varyproportionally as a function of the distance of the contact point fromthe conductive traces.

The touchpad may further include a first pair of timing capacitors eachconnected to a respective one of the first pair of conductive traces anda second pair of timing capacitors each connected to a respective one ofthe second pair of conductive traces. The touchpad may also include amicroprocessor operative with the timing capacitors for controlling andmonitoring charging time of the timing capacitors to determine theposition and asserted pressure of the object on the touch surface of thepad.

Further, in carrying out the above objects, a method for providing asignal to a computer representative of a position and asserted pressureof an object touching a touchpad is provided. The method is for use witha touchpad having X and Y position and Z pressure sensitive sensorlayers in which the X and Y sensor layers come into contact at a contactpoint when the object touches the touchpad. The method includesproviding a pair of spaced apart X conductive traces running acrossopposite ends of the X sensor layer along a Y direction such that aresistance RX between the opposite ends of the X sensor layer connectsthe pair of X conductive traces. Then a pair of spaced apart Yconductive traces running across opposite ends of the Y sensor layeralong an X direction generally perpendicular to the Y direction isprovided such that a resistance RY between the opposite ends of the Ysensor layer connects the pair of Y conductive traces is provided.

The X conductive traces are then driven to a given voltage so thatcurrent flows from the contact point through a variable pressureresistance RZ across variable position resistances to the pair of Yconductive traces. The position of the object is then determined along aY direction on the Y sensor layer as a function of the current flowingfrom the contact point to the pair of Y conductive traces. The currentvaries as a function of the variable pressure resistance RZ and thevariable position resistances connecting the pair of Y conductive tracesto the contact point.

The Y conductive traces are then driven to a given voltage so thatcurrent flows from the contact point through a variable pressureresistance RZ across variable position resistances to the pair of Xconductive traces. The position of the object is then determined alongan X direction on the X sensor layer as a function of the currentflowing from the contact point to the pair of X conductive traces. Thecurrent varies as a function of the variable pressure resistance RZ andthe variable position resistances connecting the pair of X conductivetraces to the contact point. The Z pressure of the object touching thetouchpad is then determined from the currents flowing from the contactpoint to the pairs of X and Y conductive traces.

Determining the position of the object along the X and Y directions maybe performed by determining the time required for the current to chargetiming capacitors connected to the respective ones of the X and Yconductive traces.

The advantages accruing to the present invention are numerous. Forinstance, the touchpad of the present invention provides a touchpad forproviding a signal to a computer indicative of the location and appliedpressure of an object touching the touchpad. The touchpad has theability to measure the gradation of pressure applied on the touchpad andoffer dynamic-sensing features.

These and other features, aspects, and embodiments of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall block diagram of a touchpad assembly of the presentinvention employed with a computer;

FIG. 2 is a top plan view of a touchpad of the present invention;

FIG. 3 illustrates the electrical resistance associated with a positionsemiconductor resistance sensor of the touchpad;

FIG. 4 is a top view of X and Y position semiconductor resistancesensors of the touchpad unfolded with associated pairs of X and Yconductive leads;

FIG. 5 is a side view of the X and Y position semiconductor resistancesensors folded together;

FIG. 6 is FIG. 5 rotated by 90 degrees;

FIG. 7 illustrates a light touch activating the X and Y positionsemiconductor resistance sensors;

FIG. 8 illustrates a heavy touch activating the X and Y positionsemiconductor resistance sensors;

FIG. 9 is a schematic circuit diagram of the electronic circuitry of thetouchpad assembly;

FIG. 10a is a schematic circuit diagram when conductive traces disposedon the opposite sides of the X position semiconductor resistance sensorare driven to the same electric potential;

FIG. 10b is a schematic circuit diagram of the left branch of thecircuit diagram of FIG. 10a;

FIG. 10c is a schematic circuit diagram of the right branch of thecircuit diagram of FIG. 10a;

FIG. 11a is a schematic circuit diagram when conductive traces disposedon the opposite sides of the Y position semiconductor resistance sensorare driven to the same electric potential;

FIG. 11b is a schematic circuit diagram of the left branch of thecircuit diagram of FIG. 11a;

FIG. 11c is a schematic circuit diagram of the right branch of thecircuit diagram of FIG. 11a;

FIG. 12 illustrates a single tap selection gesture, a double tapexecution gesture, and a tap and drag dragging gesture performed on thetouchpad;

FIG. 13 is a flow diagram representing operation of a system and methodof linking a touchpad to different functions within a graphic userinterface operating on a computer; and

FIG. 14 is a flow diagram representing operation of a system and methodfor providing a signal to a computer representative of an objecttouching a touchpad.

BEST MODES FOR CARRYING OUT THE INVENTION

Referring now to FIGS. 1 and 2, a force sensing semiconductive touchpadassembly 10 of the present invention is shown. Touchpad assembly 10 is atouch-sensitive user input device. Touchpad assembly 10 includes atouchpad 12 and a microcontroller 14. Touchpad assembly 10 providesinformation indicative of the position of an operator's finger or stylustouching touchpad 12 to a computer 16 through a communications link 18.Touchpad assembly 10 also provides information indicative of the actualamount of pressure applied by an operator on touchpad 12. Computer 16processes the information to control functions of a graphical userinterface 20 producing a display 22 having a cursor 24. An operator mayalso select commands or manipulate graphically portrayed objects ingraphical user interface 20 with touchpad assembly 10. Preferably,touchpad assembly 10 is built into a computer keyboard and positionedbelow the space bar of the keyboard so that an operator can manipulatetouchpad 12 with his or her thumbs. Alternatively, touchpad assembly 10is a portable device like a mouse.

Touchpad 12 includes a cursor control region 26, a pan control region28, and a scroll control region 30. Pan control region 28 ishorizontally disposed adjacent cursor control region 26. Scroll controlregion 30 is vertically disposed adjacent cursor control region 26.

When an operator touches cursor control region 26, touchpad 12 providesa cursor control signal to computer 16 based on the position andpressure applied by the operator in the cursor control region. Inresponse to the cursor control signal, computer 16 controls the positionof cursor 24 in graphical user interface 20. Similarly, when theoperator touches pan control region 28, touchpad 12 provides a pancontrol signal to computer 16 based on the position and force applied bythe operator in the pan control region. In response to the pan controlsignal, computer 16 causes at least a portion of graphical userinterface 20 to pan. Lastly, scroll control region 30 provides a scrollcontrol signal to computer 16 which causes graphical user interface 20to scroll upon the operator touching the scroll control region.

Touchpad 12 further includes a function region 31. Function region 31comprises a first control region 32, a second control region 34, a thirdcontrol region 36, a fourth control region 38, and a fifth controlregion 40. Each of these control regions are linked to functions ingraphical user interface 20. Thus, upon touching one of these controlregions, touchpad 12 provides a control signal to computer 16 which thenperforms the function. Function region 31, which is vertically disposedadjacent cursor control region 26, is covered with a template withgraphic designs. The graphic designs are representative of the functionsassociated with the control regions. All of the control regions,including cursor control region 26, pan control region 28, and scrollcontrol region 30, are portions of a single touchpad member oralternatively, are comprised of separate touchpad members.

In a preferred embodiment, first control region 32 is linked to afunction for controlling cursor 24 in graphical user interface 20. Also,preferably, second control region 34 is linked to a pan function andthird control region 36 is linked to a scroll function in graphical userinterface 20.

Pan control region 28 has a left portion 42 and a right portion 44. Whenan operator touches left portion 42, graphical user interface 20 pans tothe left. Similarly, graphical user interface 20 pans to the right whenan operator touches right portion 44. A primary advantage of touchpadassembly 10 is that touchpad 12 has the capability of directly measuringthe actual pressure applied by the operator. As a result, computer 16may control a rate of panning in proportion to a variable amount ofpressure applied to pan control region 28 by an operator.

Pan control region 28 is further provided with a central portion 46located between left portion 42 and right portion 44. Computer 16controls a rate of panning in proportion to a distance of the touch ofan operator in pan control region 28 away from central portion 46.

Scroll control region 30 has an upper portion 48 and a lower portion 50.An upwards scroll of graphical user interface 20 corresponds to thetouch of an operator toward upper portion 48 of scroll control region30. A downwards scroll of graphical user interface 20 corresponds to thetouch of an operator toward lower portion 50 of scroll control region30. Like pan control region 28, scroll control region 30 is pressuresensitive. As a result, computer 16 may control a rate of panning inproportion to a variable amount of pressure applied to scroll controlregion 30 by an operator.

Scroll control region 30 is further provided with a central portion 52located between upper portion 48 and lower portion 50. Computer 16controls a rate of scrolling in proportion to a distance of the touch ofan operator in scroll control region 28 away from central portion 52.

Cursor control region 26, pan control region 28, and scroll controlregion 30 are separated by a visual cue on touchpad 12. Preferably, thevisual cue is a printed stripe. Touchpad 12 further includes raisedridges 54, 56, and 58 which separate cursor control region 26, pancontrol region 28, scroll control region 30, and function region 31.

Touchpad 12 is provided with a cover 60 having a cursor control regionpane 62, a function region pane 64, a pan control region pane 66, and ascroll control region pane 68. Panes 62, 64, and 66 form openings todesignate the various regions.

Referring now to FIGS. 3 and 4, touchpad 12 includes a positionsemiconductor resistance sensor 70. Position sensor 70 comprises an Xposition semiconductor resistance sensor 72 folded over a Y positionsemiconductor resistance sensor 74 (shown best in the unfolded view ofFIG. 4). A pair of electrically conductive X output leads or traces 76and 78 run along opposite ends of X position sensor 72. Similarly, apair of electrically conductive Y output leads or traces 80 and 82 runalong opposite ends of Y position sensor 74. X output leads 76 and 78and Y output leads 80 and 82 are oriented 90 degrees with respect toeach other. All of the leads are arranged together at 84 for connectionto position and pressure processing electronic circuitry.

Position sensors 72 and 74 are semiconductive layers having a givensurface resistivity and an associated electrical resistance. Electricalcurrent flows across position sensors 72 and 74 when a voltage potentialexists between respective output leads. For example, current flows fromX output lead 76 across X position sensor 72 to X output lead 78 whenthe X output leads are at different potentials. Similarly, current flowsfrom Y output lead 80 across Y position sensor 74 to Y output lead 82when the Y output leads are at different potentials.

Touchpad 12 provides X and Y position data for a contact location suchas point 86 based on the electrical resistance properties of X and Yposition sensors 72 and 74. To illustrate, point 86 is arbitrarilylocated on touchpad 12 and is located an arbitrary distance away fromeach output lead. Thus, a resistance is between point 86 and therespective output leads. The resistance between point 86 and an outputlead is a function of the given surface resistivity of position sensor70 and the length of the portion of the position sensor separating thepoint and the output lead.

Current flows from point 86 across position sensor 70 to an output leadwhen the output lead and the point are at different potentials. Theresistance between point 86 and an output lead is high if a largeportion of position sensor 70 separates point 86 and the output lead.Correspondingly, the resistance is low if only a small portion ofposition sensor 70 separates point 86 and the output lead.

As shown in FIGS. 3 and 4, a resistance RXH 88 is between point 86 and Xoutput lead 76 on one side of X position sensor 72 and a resistance RXL90 is between the point and X output lead 78 on the other side of the Xposition sensor. The resistances RXH 88 and RXL 90 added in series isthe X direction resistance RX. In turn, a resistance RYH 92 is betweenpoint 86 and Y output lead 80 on one side of Y position sensor 74 and aresistance RYL 94 is between the point and Y output lead 82 on the otherside of Y position sensor. The resistances RYH 92 and RYL 94 added inseries is the Y direction resistance RY. Accordingly, the resistancevariables (RXH, RXL, RYH, and RYL) depend on the position of point 86.Touchpad assembly 10 manipulates the resistance variables to determinethe position and pressure of an object touching touchpad 12.

As shown in FIG. 4, X and Y position sensors 72 and 74 are unfolded forillustrative purposes. x position sensor 72 preferably has a length inthe X direction of 1.8 inches and a length in the Y direction of 2.4inches. Y position sensor 74 preferably has a length in the X directionof 1.82 inches and a length in the Y direction of 2.4 inches. X outputleads 76 and 78 preferably have a width of 0.02 inches running along Xposition sensor 72. Y output leads 80 and 82 preferably have a width of0.03 inches running along Y position sensor. At 84, the output leads arepreferably spaced 0.01 inches from each other.

As shown in FIG. 5, X position sensor 72 and Y position sensor 74 arefolded when in use with touchpad 12. Note how X output lead 76 and Youtput leads 80 and 82 run orthogonally with respect to each other. Alsonote how Y output leads 80 and 82 are on opposite ends of Y positionsensor 74. Furthermore, X output leads 76 and 78 and Y output leads 80and 82 are positioned on opposite sides of their respective positionsensors so that they never come in direct electrical contact and resultin a short circuit. Of course, the leads may be positioned on adjacentsides of their respective position sensors as long as they are separatedby an insulator such as a piece of tape to prevent direct electricalcontact.

Still referring to FIG. 5, touchpad 12 includes a pad surface 96 and aprinted circuit board 98. Pad surface 96 is exposed for an operator totouch. Touchpad assembly 10 determines the location and pressure appliedby the operator touching a point on pad surface 96. Printed circuitboard 98 is provided with microcontroller 14 and outputs forcommunication link 18 to computer 16.

Referring now to FIG. 6, touchpad 12 has been rotated by 90 degrees fromthe side view shown in FIG. 5. Note how Y output lead 80 runs along Yposition sensor 74 from one edge to the other. Also note how X outputleads 76 and 78 are disposed on opposite ends of X position sensor 72.

In addition to the X and Y direction resistances discussed above, eachposition sensor also has a resistance associated with the Z direction.The resistance in the Z direction is a function of the resistivity andthe thickness of the position sensor. Position sensors 72 and 74 arepressure sensitive sensors as described in U.S. Pat. No. 4,489,302issued to Eventoff. The patent to Eventoff is incorporated in itsentirety herein by reference. As taught by Eventoff, the resistance ofposition sensors 72 and 74 in the Z direction varies inversely as afunction of applied pressure.

Thus, when position sensors 72 and 74 are pressed together, a resistanceRZ is produced. Touchpad 12 is a through mode device where electronsflow between the two separate X and Y position sensors 72 and 74 whenthe sensors are pressed together at contact point 86. The flow ofelectric current occurs through X and Y position sensors 72 and 74 atcontact point 86 and across the X and Y position sensors to therespective output leads.

Referring now to FIGS. 7 and 8, position sensors 72 and 74 are pressedtogether at contact point 86 when a finger 100 touches pad surface 96.If a light touch is applied by finger 100 on pad surface 96 then theresistance RZ is large. As finger 100 applies a harder touch as shown inFIG. 8, the RZ resistance decreases. In essence, the resistance RZvaries inversely on the amount of applied pressure at point 86.

Referring now to FIG. 9, the operation of touchpad assembly 10 in usingthe resistance RZ and the resistance variables (RXH, RXL, RYH, and RYL)to determine the position and applied pressure of an object touchingtouchpad 12 will be described. Touchpad 12 is connected tomicrocontroller 14 at four nodes. The nodes are RXH node 102, RXL node104, RYH node 106, and RYL node 108. Resistance RXH 88 and resistanceRXL 90 are in series between RXH node 102 and RXL node 104. ResistanceRXH 88 and resistance RXL 90 added together equals a resistance RX 110.Similarly, resistance RYH 92 and resistance RYL 94 are in series betweenRYH node 106 and RYL node 108. Resistance RYH 92 and resistance RYL 94added together equals a resistance RY 112. A resistance RZ 114 isconnected between resistance RX 110 and resistance RY 112.

Between each node and microcontroller 14 is a capacitor and a resistor.The capacitor is parallel with respect to the resistor andmicrocontroller 14. Thus, the capacitor creates a capacitor bridge. Forinstance, between RXL node 104 and the first port of microcontroller 14is a timing capacitor C1 and a resistor R1. Timing capacitor C1 isparallel with respect to Rl and microcontroller 14. Timing capacitorsC2, C3, and C4 and resistors R2, R3, and R4 are similarly arranged withrespect to associated nodes and ports of microcontroller 14.

Microprocessor 14 performs measurements on the amount of time that thecapacitors need to charge to a given voltage. As known to those ofordinary skill in the art and freshman physics students, the amount ofcharging and discharging time for a capacitor in a closed circuit variesas a function of the resistance in series with the capacitor. Thecharging and discharging times are a function of the product of theresistance (R) of the resistor multiplied by the capacitance (C) of thecapacitor. The product RC is known as the capacitive time constant.

In operation, as pressure is applied to touchpad 12 at contact point 86,resistance RZ 114 changes inversely as a function of the pressureapplied. As described above, resistance RXH 88 and resistance RXL 90 areproportional with respect to the horizontal position of contact point 86along the X direction of touchpad 12. Correspondingly, resistance RYH 92and resistance RYL 94 are proportional with respect to the verticalposition of contact point 86 along the Y direction of touchpad 12.

Microprocessor 14 preferably includes one Microchip PIC 16C622microcontroller. Microprocessor 14 performs positional and pressuremeasurements as follows. First, the nodes (102, 104, 106, 108) aredriven by microprocessor 14 to 0 volts for a sufficient time to allowtiming capacitors C1, C2, C3 and C4 to fully discharge. Then RXH node102 and RXL node 104 are driven to a given voltage VCC by microprocessor14. Preferably, the given voltage VCC is the supply voltage of +5 volts.Timing capacitors C3 and C4 charge at a rate proportional to theresistance between it and VCC and its capacitance. The resistance isdetermined by the position and applied pressure on contact point 86.

Resistors R1, R2, R3, and R4 are preferably 470 ohm current limitingresistors to prevent the maximum output current from microprocessor 14to approximately 10 milliamps maximum. The 10 milliamps is well belowthe microcontroller device specification. Timing capacitors C1, C2, C3,and C4 are preferably 0.047 micro farad.

FIG. 10a shows a circuit 116 for touchpad 12 when RXH node 102 and RXLnode 104 are driven to VCC. A current I4 flows from VCC through a leftbranch 118 of circuit 116 to timing capacitor C4. Similarly, a currentI3 flows through a right branch 120 of circuit 116 to timing capacitorC3. From Kirchoff's Voltage Law in which Voltage (V)=Current(I)*Resistance (R), the magnitude of the currents I3 and I4 depend onthe resistance that they flow across. In turn, the time that it takesthe timing capacitors C3 and C4 to charge depends on the magnitude ofthe currents I3 and I4.

As shown in FIG. 10b, timing capacitor C4 and a resistance equaling thesummation of resistance RZ 114 and resistance RYL 94 are in series.Similarly, as shown in FIG. 10c, timing capacitor C3 and a resistanceequaling the summation of the resistance RZ 114 and resistance RYH 92are in series.

Microprocessor 14 measures the time that it takes timing capacitors C3and C4 to charge to a predetermined voltage after driving RXH node 102and RXL node 104 to VCC. Preferably, microprocessor 14 logs the timeTRYH when timing capacitor C3 charges to 3 volts. The voltage of timingcapacitor C3 is monitored at RYH node 106. Microprocessor 14 also logsthe time TRYL when timing capacitor C4 charges to 3 volts. The voltageof timing capacitor C4 is monitored at RYL node 108. If timingcapacitors C3 and C4 do not charge to the predetermined voltage within 8milliseconds then the measurement process is aborted due to inadequateforce to activate.

Next microprocessor 14 drives the nodes (102, 104, 106, 108) to 0 voltsfor a sufficient time to allow timing capacitors C3 and C4 to fullydischarge. Microprocessor 14 then drives RYH node 106 and RYL node 108to VCC. Timing capacitors C1 and C2 then charge at a rate proportionalto the resistance between it and VCC and its capacitance.

FIG. 11a shows a circuit 122 for touchpad 12 when RYH node 106 and RYLnode 108 are driven to VCC. A current I1 flows from VCC through a leftbranch 124 of circuit 122 to timing capacitor C1. Similarly, a currentI2 flows through a right branch 126 of circuit 122 to timing capacitorC2. The magnitude of the currents I1 and I2 depend on the resistancethat they flow across. In turn, the time that it takes the currents I1and I2 to charge timing capacitors C1 and C2 depends on the resistance.

As shown in FIG. 11b, timing capacitor C1 and a resistance equaling thesummation of resistance RZ 114 and resistance RXL 90 are in series.Similarly, as shown in FIG. 11c, timing capacitor C2 and a resistanceequaling the summation of the resistance RZ 114 and resistance RXH 88are in series.

Microprocessor 14 measures the time that it takes timing capacitors C1and C2 to charge to the predetermined voltage of 3 volts after drivingRYH node 106 and RYL node 108 to VCC. Microprocessor 14 logs the timeTRXL when timing capacitor C1 charges to 3 volts. The voltage of timingcapacitor C1 is monitored at RXL node 104. Microprocessor 14 also logsthe time TRXH when timing capacitor C2 charges to 3 volts. The voltageof timing capacitor C2 is monitored at RXH node 102. If timingcapacitors C1 and C2 do not charge to the predetermined voltage within 8milliseconds then the measurement process is aborted due to inadequateforce to activate.

With the time measurements TRXH, TRXL, TRYH, and TRYL, microprocessor 14computes the position and applied pressure on contact point 86. Theposition and pressure data is then converted to the appropriatecommunications format and transmitted to computer 16 throughcommunications link 18.

As an overview, if the time measurements TRYH is equal to TRYL, then thevertical position of contact point 86 is directly in the middle oftouchpad 12 along the Y axis. If TRYP is greater than TRYL, then thevertical position of contact point 86 is towards the bottom of touchpad12 along the Y axis. Conversely, if TRYL is greater than TRYH, then thevertical position of contact point 86 is towards the top of touchpad 12along the Y axis.

For the X axis, if TRXH is equal to TRXL then the horizontal position ofcontact point 86 is directly in the middle of touchpad 12 along the Xaxis. If TRXH is greater than TRXL, then the horizontal position ofcontact point 86 is towards the left side of touchpad 12 along the Xaxis. If TRXL is greater than TRXH, then the horizontal position ofcontact point 86 is towards the right side of touchpad 12 along the Yaxis.

Microprocessor 14 performs the following calculations to determine thevertical and horizontal position of an object touching touchpad 12 alongwith the applied pressure of the object.

Constants

Tmaxry=Proportional to maximum amount of resistance along the Y axis oftouchpad 12 and capacitance of a timing capacitor.

Tmaxrx=Proportional to maximum amount of resistance along X axis oftouchpad 12 and capacitance of a timing capacitor.

Calculations

1. Tdeltay=TRYL−TRYH

2. Tdeltax=TRXL−TRXH

3. Vertical Position=(Tdeltay+(0.5*Tmaxry))/Tmaxry

4. Horizontal Position=(Tdeltax+(0.5*Tmaxrx))/Tmaxrx

5.Tforce1=TRYL+TRYH−Tmaxry−2*(1/((Tmaxrx/(0.5*(Tmaxrx+Tdeltax)))+(Tmaxrx/(0.5*(Tmaxrx−Tdelatx))))

6.Tforce2=TRXL+TRXH−Tmaxrx−2*(1/((Tmaxry/(0.5*(Tmaxry+Tdeltay)))+(Tmaxry/(0.5*(Tmaxry−Tdelaty))))

7. Tforce=(Tforce1+Tforce2)/2

Thus, Vertical Position indicates the location of the object along the Yaxis of touchpad 12. Horizontal Position indicates the location of theobject along the X axis of touchpad 12. Tforce indicates the appliedpressure of the object at the location. This data may be manipulatedfurther by computer 16 to perform more advanced processing forapplications such as gesture recognition.

Tforce is then converted to pressure based on a computed table ofconversion factors. The time measurements are preferably performed bymicroprocessor 14 forty times per second. As shown, the simplicity ofthe circuit yields ratio metric results thus absolute values of R1, R2,R3, and R4, and C1, C2, C3, and C4 are not critical in design andconstruction. As readily seen, the arrangement of microprocessor 14 andtiming capacitors C1, C2, C3, and C4, and resistors R1, R2, R3, and R4is much simpler and cheaper than the complex electronic circuitry usedby the prior art touchpads introduced earlier.

Touchpad 12 is capable of formatting X and Y relationships resolved inthe range of 1,000 lines per inch. Z force information (downwardpressure on touchpad 12) is discriminated into 256 levels. A problemwith the pressure sensitive force transducer described by Eventoff foruse with touchpad 12 is that the resistance RZ is much larger than theresistances RX and RY. Thus, the resistance RZ is the dominant variablefor the charging time of a timing capacitor. Because the coupling of Xposition sensor 72 and Y position sensor 74 must occur through theresistance RZ, the pressure transducer described by Eventoff results inpoor positional control. To properly be able to provide positionalinformation (X, Y) along with pressure (Z) information, the resistiveink formulation of position sensors 72 and 74 have been altered from theformulation used by Eventoff.

Position sensors 72 and 74 are a semiconductive ink consisting of fourbasic components. The components are carbon, resin, filler, and solvent.The primary difference between the force transducer of Eventoff andposition sensors 72 and 74 is an improved filler material, stannousoxide. Prior art formulations use an approximate 3:1 ratio of filler tothe appropriate blend of carbon/resin/solvent mixture. Position sensors72 and 74 use only an approximate 20% loading of filler to thecarbon/resin/solvent blend. The reduced amount of filler quickly dropsthe initial resistance RZ down to a lower range to accurately calculatethe position of contact point 86. Thus, upon contact, the resistance RZis of the same magnitude of the resistances RX and RY. Specifically, theresistance RZ falls within a range of 4 to 2 Kilo ohms when theactivation force is between 15 to 100 grams. At 10 grams, the resistanceRZ is low enough to allow conduction. Prior art formulations have aresistance RZ falling within the range of 20 to 10 Kilo ohms when theactivation force is between 15 and 100 grams. Resistances in this rangeare far greater than the resistances RX and RY. At 10 grams, theresistance RZ is too high to allow conduction or meaningful positionalinformation. As a result, a primary advantage of the present inventionis the low activation force of about 10 grams required for touchingtouchpad 12.

Referring now to FIG. 12, touchpad 12 includes selection, execution, anddrag functions to fully emulate mouse cursor control functions. Theselection, execution, and drag functions are implemented by emulatingthe generic click, double click, and click and drag functions performedby the left mouse button as defined in typical computer systems.

A feature of touchpad assembly 10 is that during normal operation,pressure threshold settings for different size and shape pressureactivators are automatically adjusted. A pressure threshold setting isaccomplished by long term averaging where the data points are gatheredduring actual operation of the device. The pressure threshold setting isthen used to determine if the tap and click operations have beenasserted with a pressure that is proportional to the average pressureused.

Another feature of touchpad assembly 10 is that touchpad 12 has an edgecontinuation motion feature for assisting in drag operations. Duringdragging, when an edge of touchpad 12 has been reached cursor 24 isscrolled at a fixed rate and angle based on the rate and angle of thedrag just prior to reaching the edge of the touchpad. The edgecontinuation motion terminates whenever the pressure activation isremoved, or the activation is moved from the edge of touchpad 12.

Touchpad assembly 10 may employ filtering algorithms for cursor control.Touchpad 12 is sensitive enough to measure the pulse of an operator'sheart when the operator touches touchpad 12. Thus, filtering algorithmswhich filter out all but the pressure centroid are used to enhancecursor control. Touchpad assembly 10 may also employ a form ofpredictive filtering to anticipate where an object touching touchpad 12is headed. This is related primarily to movement across touchpad 12 andfiltering produces a smooth transition.

Another advantage of touchpad assembly 10 includes minimal powerconsumption. It is estimated that touchpad assembly 10 uses 85% lesspower than capacitive touchpads which must always have chargedcapacitors. In a typical application in which a touchpad is used about10% of the time, touchpad assembly consumes about 260 micro amps perhour. Prior art capacitive touchpads consume about 2,200 to 10,000 microamps per hour.

Referring now to FIG. 13, a flow diagram 130 representing operation ofthe touchpad apparatus and method according to the present invention isshown. In general, flow diagram 130 links a touchpad to differentfunctions with a graphical user interface operating on a computer. Flowdiagram 130 begins with block 132 mapping a surface of a touchpadmember. The surface is mapped to define a cursor control area and afunction area. Block 134 then receives a signal. The signal isindicative of an initial user contact location and a movement on thesurface of the touchpad member.

Block 136 then compares the initial user contact location with thedefined cursor control area if the initial user contact falls within thedefined cursor control region. In response to block 136, block 138 thenmoves a cursor within the graphical user interface in a manner thatcorresponds to the movement on the surface of the touchpad member. Block140 then compares the initial user contact location with the definedfunction area if the user contact falls within the function area. Inresponse to block 140, block 142 performs a corresponding functionwithin the graphical user interface.

Referring now to FIG. 14, a flow diagram 150 representing operation ofthe touchpad apparatus and method according to the present invention isshown. In general, flow diagram 150 provides a signal to a computerrepresentative of a position and applied pressure of an object touchinga touchpad. Flow diagram 150 begins with block 152 providing a pair ofspaced apart X conductive traces. The X conductive traces run acrossopposite ends of the X sensor layer in a Y direction such that aresistance RX between the opposite ends of the X sensor layer connectsthe pair of spaced apart X conductive traces. Block 154 then provides apair of spaced apart Y conductive traces. The Y conductive traces runacross opposite ends of the Y sensor layer in an X direction generallyperpendicular to the Y direction such that a resistance RY between theopposite ends of the Y sensor layer connects the pair of spaced apart Yconductive traces.

Block 156 then drives the X conductive traces to a given voltage so thatcurrent flows from the contact point through a variable pressureresistance RZ across variable position resistances to the pair of Yconductive traces. Block 158 then determines the position of the objectalong a Y direction on the Y sensor layer as a function of the currentflowing from the contact point to the pair of Y conductive traces. Thecurrent varies as a function of the variable pressure resistance RZ andthe variable position resistances connecting the pair of Y conductivetraces to the contact point.

Block 160 then drives the Y conductive traces to a given voltage so thatcurrent flows from the contact point through a variable pressureresistance RZ across variable position resistances to the pair of Xconductive traces. Block 162 then determines the position of the objectalong an X direction on the X sensor layer as a function of the currentflowing from the contact point to the pair of X conductive traces. Thecurrent varies as a function of the variable pressure resistance RZ andthe variable position resistances connecting the pair of X conductivetraces to the contact point.

Block 164 then determines the applied pressure of the object touchingthe touchpad from the currents flowing from the contact point to thepairs of X and Y conductive traces.

It should be noted that the present invention may be used in a widevariety of different constructions encompassing many alternatives,modifications, and variations which are apparent to those with ordinaryskill in the art. Accordingly, the present invention is intended toembrace all such alternatives, modifications, and variations as fallwithin the spirit and broad scope of the appended claims.

What is claimed is:
 1. A touchpad for providing a signal to a computerindicative of the location and applied pressure of an object touchingthe touchpad, the touchpad comprising: a pad having a touch surface; afirst sensor layer; a first pair of spaced apart conductive tracesrunning across opposite ends of the first sensor layer in a firstdirection such that a first resistance between the opposite ends of thefirst sensor layer connects the first pair of conductive traces; asecond sensor layer; and a second pair of spaced apart conductive tracesrunning across opposite ends of the second sensor layer in a seconddirection generally perpendicular to the first direction such that asecond resistance between the opposite ends of the second sensor layerconnects the second pair of conductive traces; wherein the first andsecond sensor layers come into contact at a contact point when an objectasserts a pressure on the touch surface of the pad, wherein the contactpoint is connected to each conductive trace by a pressure resistanceassociated with the first and second sensor layers and positionresistances of the first and second sensor layers, wherein the pressureresistance varies as a function of the pressure asserted and theposition resistances vary as a function of the distance of the contactpoint from the conductive traces.
 2. The touchpad of claim 1 furthercomprising: a first pair of timing capacitors each connected to arespective one of the first pair of conductive traces; and a second pairof timing capacitors each connected to a respective one of the secondpair of conductive traces.
 3. The touchpad of claim 2 furthercomprising: a microprocessor operative with the timing capacitors,wherein the microprocessor controls and monitors charging time of thetiming capacitors to determine the position and asserted pressure of theobject on the touch surface of the pad.
 4. The touchpad of claim 3wherein: the charging time of a timing capacitor is a function of thepressure resistance and the position resistance connecting the contactpoint to the one of the conductive traces that the timing capacitor isconnected.
 5. The touchpad of claim 3 wherein: the microprocessor drivesthe first pair of conductive traces to a given voltage so that currentflows from the contact point through the pressure resistance, theposition resistances, and the second pair of conductive traces to thesecond pair of timing capacitors, wherein the microprocessor monitorsthe charging time for the current to charge the second pair of timingcapacitors to determine the position of the object along the firstdirection.
 6. The touchpad of claim 5 wherein: current flows from thecontact point through the pressure resistance, a position resistanceconnecting the contact point and one of the second pair of conductivetraces, the one of the second pair of conductive traces, and then to oneof the second pair of timing capacitors, wherein the microprocessormonitors the charging time for the current to charge the one of thesecond pair of timing capacitors to determine the distance of the objectfrom the one of the second pair of conductive traces along the firstdirection.
 7. The touchpad of claim 6 wherein: current flows from thecontact point through the pressure resistance, a position resistanceconnecting the contact poit and the other one of the second pair ofconductive traces, the other one of the second pair of conductivetraces, and then to the other one of the second pair of timingcapacitors, wherein the microprocessor monitors the charging time forthe current to charge the other one of the second pair of timingcapacitors to determine the distance of the object from the other one ofthe second pair of conductive traces along the first direction.
 8. Thetouchpad of claim 3 wherein: the microprocessor drives the second pairof conductive traces to a given voltage so that current flows from thecontact point through the pressure resistance, the position resistances,and the first pair of conductive traces to the first pair of timingcapacitors, wherein the microprocessor monitors the charging time forthe current to charge the first pair of timing capacitors to determinethe position of the object along the second direction.
 9. The touchpadof claim 8 wherein: current flows from the contact point through thepressure resistance, a position resistance connecting the contact pointand one of the first pair of conductive traces, the one of the firstpair of conductive traces, and then to one of the first pair of timingcapacitors, wherein the microprocessor monitors the charging time forthe current to charge the one of first pair of timing capacitors todetermine the distance of the object from the one of the first pair ofconductive traces along the second direction.
 10. The touchpad of claim9 wherein: current flows from the contact point through the pressureresistance, a position resistance connecting the contact point and theother one of the first pair of conductive traces, the other one of thefirst pair of conductive traces, and then to the other one of the firstpair of timing capacitors, wherein the microprocessor monitors thecharging time for the current to charge the other one of the first pairof timing capacitors to determine the distance of the object from theother one of the first pair of conductive traces along the seconddirection.
 11. The touchpad of claim 1 wherein: the pressure resistancefalls within a range having the same order of magnitude of the first andsecond resistances of the first and second sensor layers when theasserted pressure is between 15 to 100 grams.
 12. The touchpad of claim1 wherein: the pressure resistance enables conduction of current whenthe asserted pressure is around 10 grams.
 13. The touchpad of claim 1wherein: each of the sensor layers comprise carbon, resin, filler, andsolvent, wherein each of the sensor layers have a 1:5 ratio of thefiller to a blend of the carbon, the resin, and the solvent.
 14. Thetouchpad of claim 13 wherein: the filler is stannous oxide.
 15. Atouchpad assembly for providing a signal to a computer indicative of thelocation and applied pressure of an object touching the touchpadassembly, the touchpad assembly comprising: a pad having a touchsurface; a first sensor layer; a first pair of spaced apart conductivetraces running across opposite ends of the first sensor layer in a firstdirection such that a first resistance between the opposite ends of thefirst sensor layer connects the first pair of conductive traces; asecond sensor layer; a second pair of spaced apart conductive tracesrunning across opposite ends of the second sensor layer in a seconddirection generally perpendicular to the first direction such that asecond resistance between the opposite ends of the second sensor layerconnects the second pair of conductive traces; the second sensor layerbeing disposed beneath the first sensor layer such that the first andsecond sensor layers come into contact at a contact point when an objectasserts a pressure on the touch surface of the pad, wherein the contactpoint is connected to each conductive trace by a pressure resistanceassociated with the first and second sensor layers and positionresistances of the first and second sensor layers, wherein the pressureresistance varies inversely as a function of the pressure asserted andthe position resistances vary proportionally as a function of thedistance of the contact point from the conductive traces; a first pairof timing capacitors each connected to a respective one of the firstpair of conductive traces; a second pair of timing capacitors eachconnected to a respective one of the second pair of conductive traces;and a microprocessor operative with the timing capacitors, wherein themicroprocessor controls and monitors charging time of the timingcapacitors to determine the position and asserted pressure of the objecton the touch surface of the pad.
 16. The touchpad of claim 15 wherein:the charging time of a timing capacitor is a function of the pressureresistance and the position resistance connecting the contact point tothe one of the conductive traces that the timing capacitor is connected.17. A touchpad assembly for providing a signal to a computer indicativeof the location and applied pressure of an object touching the touchpadassembly, the touchpad assembly comprising: a pad having a touchsurface; an X position sensor layer having a pair of spaced apart Xconductive traces running across opposite ends of the X sensor layeralong a Y direction such that a resistance RX between the opposite endsof the X sensor layer connects the pair of X conductive traces; a Yposition sensor layer having a pair of spaced apart Y conductive tracesrunning across opposite ends of the Y sensor layer along an X directiongenerally perpendicular to the Y direction such that a resistance RYbetween the opposite ends of the Y sensor layer connects the pair of Yconductive traces, wherein the Y sensor layer is disposed adjacent the Xsensor layer such that the X and Y sensor layers come into contact at acontact point when an object asserts a pressure on the touch surface ofthe pad, wherein the contact point is connected to each conductive traceby a pressure resistance RZ associated with the X and Y sensor layersand position resistances of the X and Y sensor lavers, wherein thepressure resistance RZ varies as a function of the pressure asserted andthe position resistances vary as a function of the distance of thecontact point from the conductive traces; a first pair of timingcapacitors each connected to a respective one of the pair of Xconductive traces; a second pair of timing capacitors each connected toa respective one of the pair of Y conductive traces; and amicroprocessor operative with the timing capacitors, wherein themicroprocessor controls and monitors charging time of the timingcapacitors to determine the position and asserted pressure of the objecton the touch surface of the pad.
 18. A method for providing a signal toa computer representative of a position and asserted pressure of anobject touching a touchpad having X and Y position sensor layers,wherein the X and Y sensor layers are Z pressure sensitive and come intocontact at a contact point when the object touches the touchpad, themethod comprising: providing a pair of spaced apart X conductive tracesrunning across opposite ends of the X sensor layer along a Y directionsuch that a resistance RX between the opposite ends of the X sensorlayer connects the pair of X conductive traces; providing a pair ofspaced apart Y conductive traces running across opposite ends of the Ysensor layer along an X direction generally perpendicular to the Ydirection such that a resistance RY between the opposite ends of the Ysensor layer connects the pair of Y conductive traces; driving the Xconductive traces to a given voltage so that current flows from thecontact point through a pressure resistance RZ across positionresistances to the pair of Y conductive traces; determining the positionof the object along a Y direction on the Y sensor layer as a function ofthe current flowing from the contact point to the pair of Y conductivetraces, wherein the current varies as a function of the pressureresistance RZ and the position resistances connecting the pair of Yconductive traces to the contact point; driving the Y conductive tracesto a given voltage so that current flows from the contact point througha pressure resistance RZ across position resistances to the pair of Xconductive traces; determining the position of the object along an Xdirection on the X sensor layer as a function of the current flowingfrom the contact point to the pair of X conductive traces, wherein thecurrent varies as a function of the pressure resistance RZ and theposition resistances connecting the pair of X conductive traces to thecontact point; and determining the Z pressure of the object touching thetouchpad from the currents flowing from the contact point to the pairsof X and Y conductive traces.
 19. The method of claim 18 wherein:determining the position of the object along a Y direction on the Ysensor layer as a function of the current flowing from the contact pointto the pair of Y conductive traces comprises determining the timerequired for the current to charge a pair of timing capacitors connectedto respective ones of the pair of Y conductive traces.
 20. The method ofclaim 18 wherein: determining the position of the object along an Xdirection on the X sensor layer as a function of the current flowingfrom the contact point to the pair of X conductive traces comprisesdetermining the time required for the current to charge a pair of timingcapacitors connected to respective ones of the pair of X conductivetraces.
 21. The touchpad of claim 1 wherein: the pressure resistancevaries inversely as a function of the pressure asserted on the touchsurface of the pad.
 22. The touchpad of claim 1 wherein: the positionresistances vary proportionally as a function of the distance of thecontact point from the conductive